Abstract
IN a recent communication1 we indicated the importance of planarity of dye molecules for the absorption of light and for photographic sensitizing. A further survey of cyanine dyes has shown this to be general; moreover, we find that dyes capable of planar form, but having strain on bond angles, show a negative temperature coefficient of absorption- in solution. Increase of rotational-vibrational energy in the molecule overcomes the strain and relaxes the structure to a non-planar form. The activation heat can be equated to the potential energy of strain which is removed.
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SHEPPARD, S., LAMBERT, R. & WALKER, R. Optical Sensitizing of Silver Halides by Dyes. Nature 145, 969–970 (1940). https://doi.org/10.1038/145969a0
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DOI: https://doi.org/10.1038/145969a0
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